The present invention pertains to chromic oxide powder for a sputtering target capable for providing a high-purity and high-density sputtering target that does not generate cracks, and to a sputtering target sintered using such chromic oxide powder.
Chromic oxide or a sintered compact target containing chromic oxide is employed as a target material used for forming, via sputtering, thin films or layers such as an abrasion-resistant protective film, a magnetic recording medium or a magnetic recording medium base film of a thermal head; a black matrix film of a liquid crystal display (LCD) panel; a heat element base film; a dielectric film for a phase-change optical recording medium and the like.
Generally, chromic oxide or a target containing chromic oxide usually cracks easily, and is of low density and low purity. When a target has low density or low purity, such target affects the characteristics of the thin film in various ways.
When the purity is low and there are many impurities, such impurities often become the source for the generation of particles and nodules during sputtering, and cause the occurrence of abnormal discharge and variation in the deposition speed and film composition.
In addition, since the deterioration of density increases pores, coarsens crystal grains, and makes the sputtered surface of the target uneven and rough, such deterioration of density will similarly cause the generation of particles and nodules during sputtering and deterioration in the characteristics of the sputtered film.
Nevertheless, as described above, since chromic oxide or a target containing chromic oxide cracks easily, there is a problem in that it is difficult to density such chromic oxide or target containing chromic oxide. Thus, there were not many cases of proactively adding chromic oxide or using chromic oxide itself as the target material.
Under the foregoing circumstances, technology has been disclosed for adjusting the porosity within the range of 35% or less upon calcinating a chromic oxide compact and manufacturing a sintered compact (for instance, refer to Patent Document 1). In this case, commercially available green chromic oxide powder is sintered as the raw material, and although this level of improvement would suffice for use as a fire-resistant material, it is evident that sufficient characteristics cannot be obtained as a sputtering target material.
An example is also disclosed of using a chrome target containing high concentration of oxygen as a base thin film of a magnetic recording medium (refer to Patent Document 2).
In this case, since chrome has a low solid solubility limit of oxygen, when a considerable amount of oxygen is contained, it will be included as chromic oxide in the form of a non-metal inclusion. If this inclusion exists randomly, the following problems have been indicated; namely, that electrification or local abnormal discharge of the chromic oxide as an inclusion will occur during the deposition by sputtering, and the inclusion will desorb from the target and float in the deposition bath.
As a measure for improving the foregoing situation, a proposal has been made for finely and uniformly dispersing chromic oxide in metal chromium. In addition, in this case, a proposal has also been made for adding chromic oxide powder to metal chromium powder, and finely and uniformly dispersing chromic oxide in metal chromium via heat treatment in a similar fashion (for instance, refer to Patent Document 3).
Nevertheless, in the foregoing cases, since the problems of purity of the chromic oxide itself and low density of the target resulting from the inclusion of chromic oxide have not been resolved, these technologies do not offer a fundamental solution for the manufacture of sputtering targets containing chromium oxide.
In addition, as a sputtering target for forming a chromic oxide thin film to be used in the black matrix of LCD panels, a proposal has been made for a manufacturing method of a chrome target comprised of metal chromium and chromic oxide (for instance, refer to Patent Document 4). In this case, since the chromic oxide is uniformly dispersed in the metal chromium and is also dense, the discharge voltage is stable and the deposition is favorable.
As a specific manufacturing example, carbide of chrome is mixed to commercially available chromic oxide and calcinated, reduced and pulverized, and thereafter subject to secondary sintering in a vacuum so as to uniformly disperse chromic oxide in the metal chromium for obtaining a dense target. Even in this case, there is no particular improvement in the purity of chromic oxide, and there is a new problem of C getting mixed in. Thus, this technology does not offer a fundamental solution for the manufacture of sputtering targets containing chromic oxide.
As a similar method, a proposal has been made wherein carbon powder is mixed to commercially available chromic oxide and calcinated, reduced and pulverized, and thereafter subject to sintering so as to uniformly disperse chromic oxide in the metal chromium for stabilizing the discharge and inhibiting the generation of particles (refer to Patent Document 5).
Nevertheless, even in this case, there is no particular improvement in the purity of chromic oxide, and there is a new problem of C getting mixed in. Thus, this technology does not offer a fundamental solution for the manufacture of sputtering targets containing chromic oxide.
Furthermore, a proposal has been made for a method of obtaining an abrasion-resistant, high-strength and high-toughness sintered compact for used in bearings or the like. Such compact is obtained by placing a mixed compact of commercially available chromic oxide and zirconium oxide in graphite powder and performing sintering thereto (for instance, refer to Patent Document 6). Even in this case, there is no particular improvement in the purity of chromic oxide, and there is a new problem of C getting mixed in from the perspective of the sintering atmosphere. Thus, this technology does not offer a fundamental solution for the manufacture of sputtering targets containing chromic oxide.
[Patent Document 1] Japanese Patent Laid-Open Publication No. S54-141808
[Patent Document 2] Japanese Patent Laid-Open Publication No. H8-73963
[Patent Document 3] Japanese Patent Laid-Open Publication No. H6-264159
[Patent Document 4] Japanese Patent Laid-Open Publication No. H8-199349
[Patent Document 5] Japanese Patent Laid-Open Publication No. H9-279334
[Patent Document 6] Japanese Patent Laid-Open Publication No. H4-132659